Prevent CAPTCHA attacks with two-factor authentication. CAPTCHA stands for ‘Completely Automated Public Turing test to tell Computers and Humans Apart’. A CAPTCHA is a type of challenge-response prompt that attempts to verify whether or not a user is human; they are used to prevent bots from interfering with typical use.

Several approaches have attempted to circumvent CAPTCHAs: cheap labor, strengthened character recognition software and bugs that bypass CAPTCHA prompts.